Abstract
Since 2012, horizontal wells at the Saleski pilot are operated with cyclic steam injection and production, recovering bitumen from the naturally fractured Grosmont carbonate reservoir. Steam has been injected in a continuous matter similar to SAGD, as well as in cyclic alteration with production from individual wells. Injection pressure is 50-60% of the overburden stress.
The Grosmont reservoir is a highly fractured carbonate rock with excellent reservoir properties (i.e. high fracture permeability and porosity). The targeted producing horizons in this reservoir are Grosmont C (20 m pay) and D (30 m pay) unit, which are separated by a laterally extensive, 1-2 m thick Marl.
The initial injectivity, which is superior to bitumen saturated sand reservoirs, can be explained by either high initial water mobility in the fractures or large system compressibility, or a combination of both.
Since the Grosmont C unit is highly fractured, it can be characterized as a box filled with sugar cubes. The ‘stiff’ cubes can locally be displaced if the fractures are allowed to drain. Geo-mechanical simulations with deterministic fractures allow the calculation of the system compressibility and Young's Modulus, based on variations of fracture and matrix properties. Results indicate that the fracture properties dominate the system characterization.
Using these insights, initial injectivity of a pilot well is matched with a reservoir model and a coupled geo-mechanical reservoir model to quantify the roles initial water mobility, matrix displacement and temperature play during cyclic operation of a naturally fractured reservoir.
